The beneficial effect of earthworms in the soil on the growth of crops is well documented. Earthworm burrows improve the soil's water intake and help aerate and loosen the soil. Earthworms also improve the nutrient supply to the crops by ingesting organic material from the surface and excreting the digested material into the topsoil. In fact, Charles Darwin, the father of the theory of evolution, studied the earthworm extensively and wrote:
When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly leveled by worms. It may be doubted if there are any other animals which have played so important a part in the history of the world as have these lowly creatures.
See also H. Hopp and C. Slater, "The Effect of Earthworms on the Productivity of Agricultural Soil", United States Department of Agriculture Journal of Agricultural Research, Vol. 78, May 15, 1949.
Unfortunately, the farming techniques of the last several decades have destroyed the earthworm population in many fields. Most destructive of these techniques is the practice of tilling the fields after harvest in the autumn, leaving little debris covering the soil during the winter. The lack of ground cover reduces the earthworm's food supply and also affects soil temperature. On ground protected by sod or crop residue, the soil temperature drops slowly in the autumn, enabling the earthworms to retreat and hibernate below the frost line. But on bare land, the soil can freeze relatively suddenly after only a day or two of cold temperatures. Sudden exposure to frozen conditions, as often happens with bare land, is often fatal to earthworms.
Within the past several years, there has been a strong movement to reduce or eliminate tillage of the soil after harvest. Commonly known as "no-till", this technique is adopted primarily as a means to reduce soil erosion. An added benefit of no-till farming is that it recreates conditions favorable to the growth of earthworms. But even though conditions are again favorable, earthworms may have to be introduced into the soil in areas where the earthworm population has completely disappeared.
Adult earthworms, as any fisherman knows, can be harvested, transported, and preserved for several days in cool, moist conditions. For example, methods of raising and harvesting earthworms are disclosed in Frijters, U.S. Pat. No. 4,513,685, issued Apr. 30, 1985. However, it is not practical to use adult earthworms to repopulate a field. Adult earthworms are relatively expensive and cannot be shipped economically because of the weight of the medium required to enable the worms to survive for several days. Accordingly, a need exists for a practical means of introducing earthworms into a field.
The encapsulation of nematodes in hydrogel matrixes has been disclosed in Nelsen, U.S. Pat. No. 4,615,883, issued Oct. 7, 1986; Nelsen, U.S. Pat. No. 4,701,326, issued Oct. 20, 1987; Nelsen, U.S. Pat. No. 4,753,799, issued Jun. 28, 1988; and Yukawa, U.S. Pat. No. 4,765,275, issued Aug. 23, 1988.
The encapsulation of seeds with various additives has been disclosed in Warner, U.S. Pat. No. 4,551,165, issued Nov. 5, 1985; Gerber, U.S. Pat. No. 4,759,151, issued Jul. 26, 1988; and Nelsen, U.S. Pat. No. 4,780,987, issued Nov. 1988.